Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.66   13.171%   $208.9816   $208.98   $209.00   $209.00  
  Purchase #2 $162.81   3.501%   $168.51   $168.51   $168.50   $168.50  
  Purchase #3 $155.69   3.736%   $161.5066   $161.51   $161.50   $161.50  
  Purchase #4 $21.27   6.234%   $22.596   $22.60   $22.60   $22.60  
  Purchase #5 $240.52   11.787%   $268.8701   $268.87   $268.85   $268.90  
  Purchase #6 $183.85   5.470%   $193.9066   $193.91   $193.90   $193.90  
  Purchase #7 $110.69   7.505%   $118.9973   $119.00   $119.00   $119.00  
  7 purchase totals = $1,059.49       $1,143.3682   $1,143.38   $1,143.35   $1,143.40